1. Field of the Invention
The present invention relates to a multicast data communication system, a data communication apparatus and a data communication method for the system, a program for causing a computer to carry out the method and a computer readable information recording medium storing therein the program.
2. Description of the Related Art
Recently, along with development of a highly-networked information society, optical fibers have been spread across the country, and, based thereon, IP networks have come to have higher data transfer rates and larger data transmission capacities. Thereby, data communication employing IP multicast communication technology has spread widely in such a form as that of services for delivering moving pictures, network game software, and so forth. As a typical example of IP multicast communication technology, a multicast method according to a protocol of a so-called PIM-SM (protocol independent multicast sparse mode), i.e., a PIM-SM BSR method is known. This method has been actually applied to many IP multicast networks.
According to the PIM-SM BSR method, a single BSR (bootstrap router) is allocated to an IP multicast domain for which IP multicast communication is carried out, for managing C-RP (rendezvous point candidate) information in the domain. In such a method, as a size of the IP multicast domain increases, a range of spread of an adverse influence tends to increase when a trouble occurs in the BSR. Furthermore, there may be a difficulty in terms of network operation, due to a difference in a management scope between the IP multicast domain and IP unicast domains included therein.
The PIM-SM BSR method is described next in detail. According to this method, from among C-BSRs (BSR candidates) existing in an IP multicast domain, one having the highest priority (when the priorities are equal, one having a largest IP address) is selected as a BSR. After that, to the BSR, each of L3-SWs or routers acting as C-RP (rendezvous point candidates) transmits its own C-RP information. After that, the BSR collects the received C-RP information, and carries out flooding therewith in a form of BSR messages in the IP multicast domain. As a result, each of the L3-SWs or the routers can recognize all the C-RP information in the IP multicast domain. Each of the L3-SWs or the routers then makes request for transmission and reception of multicast data based on the thus-recognized C-RP information, and thus, can carry out multicast data communication.
In this system, since only the single BSR is allowed to exit in the IP multicast domain, the single BSR should be in charge of the IP multicast domain even when the IP multicast domain includes a plurality of IP unicast domains.
With reference to figures, a procedure carried out until multicast communication is allowed to be actually carried out according to the PIM-SM BSR method is described next in sequence.
(1) Step 1: Operation Before a BSR is Selected
As shown in FIG. 1, each of L3-SWs (layer 3 switches) 111 through 119 acting as C-BSRs carries out flooding with a BSR message in an IP multicast domain, and thereby, they mutually compare priorities previously given thereto.
(2) Step 2: BSR Selection Operation
As a result, as shown in FIG. 2, the L3-SW 111 having the highest priority among the respective C-BSRs operates as a BSR in the IP multicast domain.
(3) Step 3: Notification of C-RP
As shown in FIG. 3, after that, each of the L3-SWs 112 through 119 other than the L3-SW 111 selected as the BSR as mentioned above carries out notification of C-RP information which the L3-SW has (MC group ‘b’, ‘c’, ‘d’, ‘e’, ‘f’, ‘g’ or ‘h’, shown) to the BSR 111. As a result, the BSR 111 can collect all the C-RP information (intra MC domain C-RP information) in the IP multicast domain. The C-RP information is information such as an IP address required to access to receive relevant information from a specific multicast information source therethrough.
(4) Step 4: Flooding with RP Information
The BSR 111 carries out flooding with all the C-RP information (intra MC domain C-RP information) in the IP multicast domain thus collected in Step 3, so as to notify of the information the respective L3-SWs 112 through 119, as shown in FIG. 4. Each of the L3-SW 112 through 119 receives this information, and thereby recognizes location information for RPs as a result of carrying out hash operation on the thus-received C-RP information (intra MC domain C-RP information). As a result, this system enters a state in which actual IP multicast communication is allowed to be carried out. In other words, in order to receive information from a specific multicast source, a receiving terminal can obtain location information for an RP through which the relevant information source is accessible, as a result of accessing any of the L3-SWs. After that, through the RP, the receiving terminal can receive the multicast information from the relevant information source.